1. Field of the Invention
The present invention relates to an apparatus and method for conveying a semiconductor frame.
2. Description of the Related Art
FIG. 3 is a perspective view of a conventional apparatus for conveying a semiconductor frame. In the process of producing a semiconductor device, the semiconductor frame 4 is conveyed by a clamp unit 5 on a movable guide rail portion 3 in the direction shown by an arrow in the drawing. The movable guide rail portion 3 is vertically moved by a vertical driving mechanism (not shown) provided under bearings 3a. The clamp unit 5 has upper and lower clamp claws 5a, 5b provided on the upstream side of the direction of conveyance and upper and lower clamp claws 5c, 5d provided on the downstream side of the direction of conveyance so as to vertically hold the semiconductor frame 4 (referred to as "lead frame" hereinafter). The clamp unit 5 also has a horizontal driving mechanism for moving the lead frame 4 in the direction of conveyance, which mechanism comprises a tapped hole 7a and a driving screw 7b which engages the threads of the tapped hole 7a. The clamp claws 5a, 5b on the upstream side and the clamp claws 5c, 5d on the downstream side are synchronously operated. A heat block 1 is provided for heating the lead frame 4 conveyed on the movable guide rail portion 3 and is fixed to a fixed board (not shown). A frame presser 2 presses or holds down the lead frame 4 on the heat block 1 and is vertically driven with predetermined timing by a driving mechanism which has the same system as that of the driving mechanism for the movable guide rail portion 3 and which is provided under a bearing 2a. The frame presser 2 is also provided with a working hole 2b. FIGS. 4A to 4G are side views showing a method of conveying the lead frame 4, and particularly showing the operation of the upper and lower clamp claws 5a, 5b of the clamp unit 5 on the upstream side of the direction of conveyance.
The operation is described below with reference to FIGS. 3 and 4A to 4G. When the lead frame 4 is conveyed to a portion between the upper and lower clamp claws 5a and 5b on the upstream side, for example, by a belt conveyor (not shown) or the like, as shown in FIG. 4A, the lower clamp claw 5b on the upstream side is upwardly moved, and the upper clamp claw 5a is downwardly moved so that the lead frame 4 is held and fixed therebetween, as shown in FIG. 4B. The clamp claws 5a, 5b are then upwardly moved while clamping the lead frame 4 therebetween, and the movable guide rail portion 3 is also upwardly moved to the same height as that of the clamp claws, as shown in FIG. 4C. The driving screw 7b is then rotated so that the lead frame 4 is conveyed for a predetermined length, as shown in FIG. 4D. Then the movable guide rail portion 3 and the clamp claws 5a, 5b are downwardly moved, as shown in FIG. 4E. The clamp claws 5a, 5b then release the lead frame 4 from the clamping, as shown in FIG. 4F. Further, the driving screw 7b is rotated in the reverse direction so that the clamp claws 5a, 5b are returned to the initial position, as shown in FIG. 4G. The operating steps shown in FIGS. 4B to 4G are repeated so that the lead frame 4 is intermittently conveyed. When the lead frame 4 is placed on the heat block 1 (refer to FIG. 3), the frame presser 2 is downwardly moved so that the lead frame 4 is urged toward the heat block 1. Wire bonding work or the like is carried out on the lead frame 4 through the working hole 2b of the frame presser 2. When the work is completed, the frame presser 2 is upwardly moved. After the operating steps shown in FIGS. 4B to 4G, the frame presser is again downwardly moved, and wire bonding work or the like is carried out in a next portion of the lead frame 4. The work is progressed by repeating the above operating steps. The movable guide rail portion 3 is upwardly moved during conveyance of the lead frame in order to avoid the contact between the upper surface of the heat block 1 and the lower surface of the lead frame 4. The clamp claws 5c, 5d on the downstream side of the direction of conveyance shown in FIG. 3 convey the lead frame 4 after the work is completed. The clamp claws 5c, 5d are operated in the same manner as the clamp claws 5a, 5b on the upstream side.
The conventional apparatus for conveying a semiconductor frame has the problems described below. Since the whole guide rail portion is vertically moved, when a semiconductor frame is conveyed by the clamp claws, the conveyance is constantly affected by the vertical movement of the guide rail portion, thereby decreasing the accuracy of conveyance of a lead frame. In addition, since the clamp unit and the lead frame must be vertically moved according to the movement of the guide rail portion after the lead frame is clamped by the clamp claws, a complicated mechanism is required.